I'm sure I've seen a few 3rd party projects related to developing drivers for specific devices, the problem is.. there are many devices, all with unique and incompatible designs.

The OpenBSD project wrote a V4L layer video(4), and a uvideo(4) driver exists for UVC web cams.. but, at the moment.. all that exists for tuners is the driver for Brooktree chipsets bktr(4) (All Analog AFAIK).

The *BSD's TV drivers are based o the ancient Meteor, reworked as bktr.

These drivers are btx78 specific.

Some individuals proposed modified drivers to work with some Pinacle boards (Conexant x78), some other individuals wrote drivers fpr the Haupppauge 150 (or is it the 250?) on FreeBSD. Indiviual work, never made it to stock. Even if some appear in the ports tree, these are not maintained, or maintained by amateurs (no pun intended).

There seems to be no interest from the *BSD side to improve or adapt drivers for the cards that appeared since 10 years ago. I guess, question of priorities.

If you need TV support, your only choice is Linux or Windows (for which the manufacturers sell the cards with a CDROM full of ... drivers).
And not all Linuces would even accept a TV card or USB dongle (can't get sound on an old -5 years- Hauppauge WinTV with a CX88x chip on Debians, just Slackware).